Oxygen has a vital role in steelmaking since most of the important reactions in steelmaking involve transfer and reaction of oxygen at an interface. There is also a tendency of oxygen to preferentially reside along the interface due to the surface active nature of the element in molten iron. The presence of oxygen at the interface lowers the interfacial tension of iron alloys and interfacial tension gradients along the interface can result in spontaneous emulsification. The emulsification itself has an effect on the kinetics of the reaction as interfacial area increases. These phenomena are the subject of a recent study by the authors. There is limited experimental knowledge of how oxygen distributes itself during reaction between iron alloys and slag. Oxygen gradients in the concentration range of these systems are very difficult to characterize at microscopic level using techniques such as electron probe micro analyzers, auger electron spectroscopy and x-ray photoelectron spectroscopy. This paper evaluates the use of secondary ion mass spectroscopy (SIMS) for characterizing oxygen using samples generated from reactions between Fe-A1 droplets and CaO-SiO2-A12O3 slag.